No mention of names, is that enough?
@coodawoodashooda No. The test for defamation is whether the words complained of reference the Claimant. This includes whether people would understand the text to refer to the Claimant even if they aren't named.
So if you wrote in your autobiography "My cookery teacher was a rapist who raped me in the school toilets", it doesn't matter that you don't name the cookery teacher because anyone who knows you, knows the period you were at school and who the cookery teacher was would understand that to mean that particular cookery teacher who they can identify was a rapist. There will be a section of the public who would know who it was about.
Pseudonyms may help but it doesn't necessarily follow that it would be a complete answer -so if you write under a pseudonym but your photo is on the book or you do book publicity, or from the facts the school and time period are ascertainable it may also mean people could identify the cookery teacher.
So if your school had unusual features about it that you wrote about that allowed the school to be identified - it was founded in 1305, it was build on a the site of a former sewage plant and the school emblem was a hamburger - again it won't matter if you've changed the name of the school and the teacher - because some people would ID the school by combining those facts and therefore the teacher.
In other cases, pseudonyms may not matter at all - say a cabinet minister is writing about their time in office and is referring to the PM, there will be a tiny number of people who that could be - allowing the PM to be identified.
Defamation is anything that causes serious harm to a person's reputation but there are defences to that including that its true; it is honest opinion/fair comment; and its publication on a matter of public interest. There are other defences but those would be the main ones likely to apply to an autobiography.
It is correct that you cannot defame the dead so if you are writing about someone who is dead you can't libel them. It's possible if you are writing personal/private stuff about them that you could infringe the privacy rights of their next of kin but in most cases it's unlikely. The biggest risk would be identifying anyone who is the victim of sexual crimes which is unlawful.
Have you written it or is this just speculative inquiring? If you have a manuscript, you could instruct a very baby barrister on a direct access basis to libel read it for you if you are that worried.
This is the current main UK law governing defamation if you are interested
www.legislation.gov.uk/ukpga/2013/26/contents/enacted